Muscle Machines

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Muscle Machines by Steven Gorseth S Spring 2006 ince the 1950s, hydraulic systems have been the main muscle of construction equipment. Driven by changes in the market over the years and in response to both government mandates and customer expectations, hydraulic systems have become more efficient, more functional and easier to use. Under the hood of today’s site preparation equipment, contractors will find from three to ten microcontrollers with several communication net
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    w  w  w .   S   i   t  e   P  r  e  p   M  a  g .  c  o  m     S  p  r   i  n  g   2   0   0   6 6 S ince the 1950s, hydraulic systems have been the mainmuscle of construction equipment. Driven by changes inthe market over the years and in response to both gov-ernment mandates and customer expectations, hydraulic sys-tems have become more efficient, more functional and easierto use. Under the hood of today’s site preparation equip-ment, contractors will find from three to ten microcontrollerswith several communication networks between them. Buthow do these essential power sources work, and how willthey be improved in the future? The Hydraulic System’s Concept and Purpose The concept behind the hydraulic system is to efficientlytransfer mechanical power to several locations on themobile vehicle. The combustion engine, whether diesel orgasoline, is the main power source. A benefit of thehydraulic system is its capability to effectively split powerto multiple distribution points rather than to several func-tional areas through separate engines and transmissions.On today’s construction site, very few vehicles with non-hydraulic solutions exist; almost all vehicles havehydraulic power steering and hydrostatic transmission.These systems are flexible with effective transfer efficien-cies, normally well above 80%, which is the main reasonthey are used. Even those vehicles such as graders thatnormally utilize mechanical or electromechanical transmis-sions are using hydrostatic front wheel assist.Further system flexibility and performance enhancementsof the hydraulic system are accomplished through the imple-mentation of electronic controllers, sensors and actuators—all together defined as the electrohydraulics system. Today’svehicles equipped with electrohydraulic systems providemore work output with less fuel usage and emissions—something every contractor (and his client) find appealing. Muscle Machines by Steven Gorseth          S        I        T        E        P       R       E       P    S  p  r   i  n  g   2   0   0   6 7 Electrohydraulic System Components The main components of an electrohydraulic system areits pumps, motors, valves, actuators, cylinders and micro-controllers.Hydraulic pumps convert rotating mechanical power intohydraulic oil flow. Pumps generate a specified hydraulic flowrate between 1 to 600 gallons per minute (GPM), and at a spe-cific system pressure range between 500 to 15,000 pounds persquare inch (PSI). Several pump technologies such as piston,vane or gear pumps are used to meet various market require-ments. Due to their small size and high power density (powerper pound), piston pumps are preferred for hydrostatic trans-mission applications. Piston pumps are utilized in higher sys-tem pressure applications (>4000 PSI). Gear pumps are nor-mally utilized on lower pressure and cost-sensitive applica-tions. The majority of vane pumps are utilized in industrialapplications such as injection molds, especially when lownoise levels are required. Custom configurations such as tan-dem pumps have also become popular; these setups providetwo independent hydraulic sources from one single package.All aspects of expected operational speed, system pressure,operational duty cycle and expected component life goals areimportant to consider when determining which pump andmotor to apply.Motors convert fluid power back into mechanical energy,and have the capability to be controlled in two speeds, eitherhigh or low, or with a continuous variable. These motors arenormally located near the vehicle wheels, drive gearboxes orany other rotational device like augers or mill grinders. Byregulating the flow of power, valves or other actuators allowthe vehicle to accomplish the intended work function,whether it is blade control on a dozer or grader; control of abucket, boom or backhoe; or soil stabilization.According to some contractors, the biggest benefit of anelectrohydraulic system is the orchestration of the completevehicle operation for best performance. Normally this isaccomplished through a controller monitoring various opera-tor input devices such as joysticks, steering panels and brakesystems along with sensors that control vehicle speed andoperation. For example, most crawlers and graders have loadcontrol capability that allow the vehicle to run the engine atthe optimum operating point on the torque curve. This maxi-mizes output torque while minimizing fuel consumption andengine emissions. However, if the vehicle runs across anunusually hard surface, such as a temporary dirt road usedby loaded trucks, then it will automatically slow down orraise the blade so the engine does not kill. Propelling/Steering Categories Most construction vehicles utilize electrohydraulics for pro-pelling and steering. The three main propel categories areclosed circuit dual path, articulation steering with propel and“Ackerman” four-wheel independent propel/steering.Crawlers, dozers and skid steer loaders use a closed cir-cuit dual path structure. In dual path applications, there aretwo separate pumps or a single tandem pump. Each pumpprovides oil flow to the motor(s) on each side of the vehicle.To use the steering function, the speed is adjusted to thewheels or tracks. The main benefit of this design is the capa-bility to counter-rotate the wheels or inside track, therebyallowing the operator to have a zero-turn radius and maneu-ver the vehicle in close quarters.Compactors, rollers and larger agricultural tractors use thepropel with articulated steering design. The benefits of thissystem are slow operation and component cost. Generally,the open circuit gear pump and valves provide a cost-effective alternative to implement smooth steering control.Some applications require a high degree of maneuverabil-ity, such as concrete pavers, aerial lifts or finishing equip-ment working close to concrete barriers or buildings. As aresult, the vehicles must work in several steer/propel modes  A look into the electrohydraulicsof construction equipment.    w  w  w .   S   i   t  e   P  r  e  p   M  a  g .  c  o  m     S  p  r   i  n  g   2   0   0   6 8 (crab, articulated, front-wheel and rear-wheel steer modes). Toaccomplish work in these modes, the vehicle must have thecapability to control the speed and direction of each drive wheelor track. This operation is generalized as the Ackerman opera-tion; the speeds and angles are controlled independently. Microcontrollers and Standards In the last six years, construction vehicles have undergone agreat advancement—that of microcontroller capability withenhanced communication support. Many construction vehi-cles already have two Controller Area Networks (CAN-buses), normally one J1939 and one proprietary CAN-buswith three to ten controllers. The CAN-bus standard hasquickly become the ethernet or communication network of mobile equipment. Many physical implementations exist inaccordance with the CAN-bus standard; most require a dis-crete 120 ohm (electric resistance measurement) resistor tobe installed at each physical end of the network. Once thisnetwork has been established, compatible devices can beadded to the network. The CAN-bus allows sensors to beshared (i.e. only one engine speed sensor reported on theCAN-bus), thus reducing both sensor and harnessing costs.The automotive market has taken distributed networking astep further by applying up to 30-plus controller, sensorand actuator nodes, and up to eight communication net-works with a few CAN-buses; some are proprietary singlewire interfaces and high speed networks for video andentertainment systems.The J1939 CAN-bus standard has expanded its specifica-tions to encompass more than engine and transmission com-munication. Several applications have added specificationsto joysticks and positioning messages. Several industriesincluding agriculture, construction and site preparation areutilizing GPS for precise functions. These industries haveprogressed by defining and ratifying standard GPS and controlmessages betweenthe task computerand the electrohy-draulic control sys-tem. They also havedefined a standardoff-board protocol,allowing various sup-pliers to compete for the off-vehicle datamanagement and control business.These standard interfaces allow con-trollers to work across a broad range of manufacturers’ offerings and vehiclesfrom multiple Original Equipment Manu-facturers (OEMs) to communicate andreceive site maps from a single man-agement system. This level of compe-tition and compatibility will encour-age OEMs and suppliers to designcost-effective solutions with a mini-mum level of compatibility for controland site management functions.The basic guidance structure utilizing GPS focuses onoperator override and manual control. These controllersare either in manual mode where they are operated oncommands from a joystick or another sensor, or in auto-matic mode where the vehicle controls command propel,steering and blade work from the task computer. The taskcomputer compares current location and mode, theninstructs propel and steering modules to correctly adjustthe vehicle control parameters. Responding to Market Trends In recent years, the site preparation, construction and agri-cultural markets have seen significant changes in designprocesses, often in response to customer expectations. Everyvehicle’s design must cater to a variety of customers, includ-ing operators, site contractors, OEMs, rental companies andgovernment agencies.Federal and state government have significantly impactedthe industry by requiring emission controls on engines; thishas forced many OEMs to utilize electronic engine con-trollers. OEMs seek to recover these additional costs by elim-inating sensor duplication and by utilizing CAN-buses tominimize the total system install cost.The construction and agricultural markets have also expe-rienced a strong push for advanced functionality like loadcontrol and machine management. This situation is similarto automobiles with anti-lock brakes. Until a few years ago,anti-lock brakes were a “nice to have” feature. Currently,anti-lock brakes are an expected standard safety feature.Other industries are exerting forces on the constructionmarket. For example, airplanes are landing and taking off with automatic assistance. Automated Guided Vehicles(AGVs) used in manufacturing plants are minimizing pro-duction costs by providing just-in-time or online stocking Muscle Machines A typical hydraulic system for an agricultural tractor using propel with articulated steering.  with no significant operator involve-ment. Farming practices utilizing GPShave increased efficiency and reducedover-fertilizing the environment. Con-struction and site preparation applica-tions are realizing efficiency gains byoptimizing work performance of indi-vidual vehicles as well as fleet manage-ment; this minimizes wasted efforts onover-compacting and effectivelydeploys vehicles and associated person-nel resources to ensure the efforts arebeing successfully completed at thelowest overall cost.With these trends, it is expectedthat worksites will become more auto-mated, breaking down the work tooptimize costs due to specialized con-tractors. With the rapid pace of change, OEMs with specific machinemanagement systems may have diffi-culty integrating all of the data into thesystems. Many customers in the con-struction market hope to see industrystandardization so suppliers of sitemanagement systems may minimizedevelopment instead of adopting sev-eral OEM specific implementations.This approach could offer significantadvantages for the country’s depart-ment of transportation, if they acceptthe design and real-time measurementinstead of an additional validationmeasurement phase. However, bothapproaches may be required until con-fidence has been established. Effects on Design Trends Due to related market trends, engi-neering departments abroad are beingdriven to implement processes thatprovide more sophisticated features atlower development costs. Three-dimensional vehicle models, for exam-ple, have shortened prototype produc-tion cycles from months to days.Today’s vehicles have a signifi-cantly more robust system through theapplication of system failure modeeffects analysis (SFMEA), process fail-ure mode effects analysis (PFMEA)and highly accelerated life testing(HALT). The purpose of these engi-neering tools is to detect design fail-ures and conflicts earlier in the designcycle in order to minimize their impacton the full development lifecycle. Cus-tomers will fare well to ask questionsabout the system’s operation require-ments and validation during the devel-opment phase.  What’s the Future? As the market continues to drive OEMsand suppliers to design more sophisti-cated machines with increased automa-tion, work output in turn has becomemore efficient. The trend to use electricmotor solutions for lower power appli-cations is accelerating, particularlywhen fuel cells become more economi-cally feasible and technology stabilizes.These enhancements in technology donot necessarily require operators tobecome highly skilled for some applica-tions. Features such as automatic orremote control operations will signifi-cantly benefit contractors in hazardousenvironmental areas or war zones.The construction industry may con-tinue to benefit from the establishmentof standard interfaces for on-vehicleinformation and off-vehicle manage-ment systems. This standardizationeffort will be challenging and time-consuming; however, the long-termbenefits have the potential to signifi-cantly reduce development costs, andpotentially allow site managers toeffectively deploy and controlresources on the jobsite independentof vehicle color or OEM. SP  Steven Gorseth is a group leader of the Sauer-Dan-foss Mobile Electronic START (proposal genera-tion) team and has participated on the J1939 com-mittee for 12 years. He may be contacted via E-mail at Santa Clara,CA 95050Toll Free Number:800.795.1001 Outside US:408.653.2070ãFax:408.748.9984European Office:+31 72 57 64 175Asia Service Center:+86 21 5046 WWW.PACIFICCREST.COM 990 RichardAvenue,Suite 110 9         S        I        T        E        P       R       E       P    S  p  r   i  n  g   2   0   0   6 Have a site prep projectyou've worked on that you’dlike to see in our pages? Call Lieca N. Hohnerat 313.886.1272or Kimberly Jensenat 248.244.6465 today.
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